Bare and dressed particles in collision theory

The bare-dressed technique is, for the first time, used in collision theory. The approach is valid for classical as well for quantum binary elastic collisions in the non relativistic regime. The same formalism can be used for inelastic collisions, when the particles undergo only a change of their internal quantum states during the collision process. All kinematic results can be obtained by a simple matrix transformation. Moreover, to make also simple and clear the results, for the inelastic collisions, the restitution coefficient formulation of inelastic processes has been used.